[Bug] "Missing required parameter: client_id." when connecting Mastodon account

[foxyseta]

I get the error message

Missing required parameter: client_id. 

on my Mastodon instance when trying to connect my liberapay account to my Mastodon one (@[email protected]). When returning back to liberapay, I hence get:

Cookie 'mastodon_social.edu.nl_Ty0fcREWi6X7h9pRJu17n1SAflttoA' not found

URL: https://liberapay.com/on/mastodon:social.edu.nl/associate?code=rOVsyhhCw28pqDCEqkec6uepiIfPAtTlHZXU9GiS1_0&state=Ty0fcREWi6X7h9pRJu17n1SAflttoA
Method: GET
Referer: None
User-Agent: b'Mozilla/5.0 (Android 10; Mobile; rv:129.0) Gecko/129.0 Firefox/129.0'
Cookies: csrf_token=[32 bytes]; session=[45 bytes]
IP address: 77.250.58.216 (NL)
Time: 2024-10-06 09:50:18.884638+00:00
Response code: 400
Response message: "Cookie 'mastodon_social.edu.nl_Ty0fcREWi6X7h9pRJu17n1SAflttoA' not found"
User: <Participant #1863527 'foxy'>
Locale: en_GB
Website version: 760
Traceback:
  state_chain.py:315 (loop)
  pando/state_chain.py:128 (render_response)
  aspen/http/resource.py:129 (render)
  aspen/simplates/simplate.py:140 (render_for_type)
  www/on/%platform/associate.spt:33 (<module>)