400 bad request when creating pay link

[hax0rbana-adam]

Problem

The error messages when there is an invalid URL does not contain the URL which is invalid nor does it explain where the URL comes from.

Steps to reproduce

1. Set up a full bitcoin node, an LND node, LNbits using LND (REST) as a back end, and install lnurlp
2. Attempt to create a pay link, filling in only the required fields
3. Observe the toast popup that says "400 BAD REQUEST"
4. Check the logs and find the log messages do not contain a URL which is invalid nor where this URL comes from (logs pasted below)

As a subsequent problem, the lightning address appears to be taken ("409 conflict" response) after the above failure to create a link. I can create a separate ticket for that if desired.

Version information

• lnurlp version: 1.0.1
• lnbits version: 1.2.1
• lnd version: 0.19.2

Logs

Aug 19 16:11:53 btc poetry[96936]: Traceback (most recent call last):
Aug 19 16:11:53 btc poetry[96936]:   File "/home/lnd/.cache/pypoetry/virtualenvs/lnbits-CTKNlgQK-py3.11/lib/python3.11/site-packages/lnurl/core.py", line 33, in encode
Aug 19 16:11:53 btc poetry[96936]:     return Lnurl(url_encode(url))
Aug 19 16:11:53 btc poetry[96936]:            ^^^^^^^^^^^^^^^^^^^^^^
Aug 19 16:11:53 btc poetry[96936]:   File "/home/lnd/.cache/pypoetry/virtualenvs/lnbits-CTKNlgQK-py3.11/lib/python3.11/site-packages/lnurl/types.py", line 178, in __init__
Aug 19 16:11:53 btc poetry[96936]:     self.url = url if url else self.__get_url__(bech32)
Aug 19 16:11:53 btc poetry[96936]:                                ^^^^^^^^^^^^^^^^^^^^^^^^
Aug 19 16:11:53 btc poetry[96936]:   File "/home/lnd/.cache/pypoetry/virtualenvs/lnbits-CTKNlgQK-py3.11/lib/python3.11/site-packages/lnurl/types.py", line 183, in __get_ur>
Aug 19 16:11:53 btc poetry[96936]:     return parse_obj_as(Union[OnionUrl, ClearnetUrl, DebugUrl], url)  # type: ignore
Aug 19 16:11:53 btc poetry[96936]:            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Aug 19 16:11:53 btc poetry[96936]:   File "pydantic/tools.py", line 38, in pydantic.tools.parse_obj_as
Aug 19 16:11:53 btc poetry[96936]:   File "pydantic/main.py", line 341, in pydantic.main.BaseModel.__init__
Aug 19 16:11:53 btc poetry[96936]: pydantic.error_wrappers.ValidationError: 3 validation errors for ParsingModel[Union[OnionUrl, ClearnetUrl, DebugUrl]]
Aug 19 16:11:53 btc poetry[96936]: __root__
Aug 19 16:11:53 btc poetry[96936]:   URL host invalid, top level domain required (type=value_error.url.host)
Aug 19 16:11:53 btc poetry[96936]: __root__
Aug 19 16:11:53 btc poetry[96936]:   URL scheme not permitted (type=value_error.url.scheme; allowed_schemes={'https'})
Aug 19 16:11:53 btc poetry[96936]: __root__
Aug 19 16:11:53 btc poetry[96936]:   invalid or missing URL scheme (type=value_error.url.scheme)
Aug 19 16:11:53 btc poetry[96936]: During handling of the above exception, another exception occurred:
Aug 19 16:11:53 btc poetry[96936]: Traceback (most recent call last):
Aug 19 16:11:53 btc poetry[96936]:   File "/home/lnd/.cache/pypoetry/virtualenvs/lnbits-CTKNlgQK-py3.11/lib/python3.11/site-packages/starlette/_exception_handler.py", line>
Aug 19 16:11:53 btc poetry[96936]:     await app(scope, receive, sender)
Aug 19 16:11:53 btc poetry[96936]:   File "/home/lnd/.cache/pypoetry/virtualenvs/lnbits-CTKNlgQK-py3.11/lib/python3.11/site-packages/starlette/routing.py", line 73, in app
Aug 19 16:11:53 btc poetry[96936]:     response = await f(request)
Aug 19 16:11:53 btc poetry[96936]:                ^^^^^^^^^^^^^^^^
Aug 19 16:11:53 btc poetry[96936]:   File "/home/lnd/.cache/pypoetry/virtualenvs/lnbits-CTKNlgQK-py3.11/lib/python3.11/site-packages/fastapi/routing.py", line 301, in app
Aug 19 16:11:53 btc poetry[96936]:     raw_response = await run_endpoint_function(
Aug 19 16:11:53 btc poetry[96936]:                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Aug 19 16:11:53 btc poetry[96936]:   File "/home/lnd/.cache/pypoetry/virtualenvs/lnbits-CTKNlgQK-py3.11/lib/python3.11/site-packages/fastapi/routing.py", line 212, in run_>
Aug 19 16:11:53 btc poetry[96936]:     return await dependant.call(**values)
Aug 19 16:11:53 btc poetry[96936]:            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Aug 19 16:11:53 btc poetry[96936]:   File "/usr/local/lnbits/data/upgrades/lnurlp-281cf5b0ebb4289f93c97ff9438abf18e01569508faaf389723144104bba2273/views_api.py", line 202,>
Aug 19 16:11:53 btc poetry[96936]:     return {**link.dict(), "lnurl": link.lnurl(request)}
Aug 19 16:11:53 btc poetry[96936]:                                     ^^^^^^^^^^^^^^^^^^^
Aug 19 16:11:53 btc poetry[96936]:   File "/usr/local/lnbits/data/upgrades/lnurlp-281cf5b0ebb4289f93c97ff9438abf18e01569508faaf389723144104bba2273/models.py", line 74, in >
Aug 19 16:11:53 btc poetry[96936]:     return lnurl_encode(url_str)
Aug 19 16:11:53 btc poetry[96936]:            ^^^^^^^^^^^^^^^^^^^^^
Aug 19 16:11:53 btc poetry[96936]:   File "/home/lnd/.cache/pypoetry/virtualenvs/lnbits-CTKNlgQK-py3.11/lib/python3.11/site-packages/lnurl/core.py", line 35, in encode
Aug 19 16:11:53 btc poetry[96936]:     raise InvalidUrl
Aug 19 16:11:53 btc poetry[96936]: lnurl.exceptions.InvalidUrl
Aug 19 16:11:53 btc poetry[96936]: 2025-08-19 16:11:53.85 | WARNING | ValueError:
Aug 19 16:11:53 btc poetry[96936]: 2025-08-19 16:11:53.85 | INFO | 127.0.0.1:52532 - "POST /upgrades/281cf5b0ebb4289f93c97ff9438abf18e01569508faaf389723144104bba2273/lnurl>
Aug 19 16:11:58 btc poetry[96936]: 2025-08-19 16:11:58.13 | INFO | 127.0.0.1:48578 - "POST /upgrades/281...REDACTED...73/lnurl>

[hax0rbana-adam]

I hacked up models.py on my test server to add some debug logs and found that the request.scheme is "http" instead of "https". The rest of the URL looks fine. Importantly it has the correct FQDN.

If I go a step further and hack lnurl() to upgrade all URLs from HTTP to HTTPS (and if it is a .onion URL, it'll be switched back to HTTP again), I can see the pay links which were apparently being created but never displayed.

Here's what my little hack looks like:

url_str = str(url).replace("http://", "https://")

So if I can figure out why the url is showing up with the wrong protocol, and figure out how to change it, I can submit a pull request to update the documentation. Any pointers would be appreciated.

[hax0rbana-adam]

I'm going to leave this open because the original issue (URL does not appear in the error message nor the logs) is still legit.

Everything else was due to configuration errors. There is documentation on the wiki which mentions X-Forwarded-Host and X-Forwarded-Proto. Once those are in place, the protocol is correct and everything works as expected.

[dni]

this will be definitly not an issue with lnbits v1.3.0 and latest lnurlp release

[tlindi]

I'm going to leave this open because the original issue (URL does not appear in the error message nor the logs) is still legit.

I'd say so too. And when new LNURLp is created by accessing LNbits with http://<privateipaddrs>:5000 and logs only:

2025-10-30 02:29:47.03 | WARNING | ValueError:
2025-10-30 02:29:47.03 | INFO | 192.168.1.104:56570 - "POST /lnurlp/api/v1/links HTTP/1.1" 400

And address list shows no added address.

Repeating pressing Create Pay Link shows error:

After this, when opening paylink extension page, there is always error:

[DoktorShift]

@dni please give it a double check and close if solved.

[dni]

its resolved by. #123