Dropbox API 409 "not_allowed" error on get_temporary_link

Based on the information you've shared, I understand you are getting a not_allowed error from the /2/files/get_temporary_link API endpoint. That error from that endpoint means:
 

not_allowedVoid The user is not allowed to request a temporary link to the specified file. For example, this can occur if the file is restricted or if the user's links are banned.

Please refer to that linked help article for more information.

Thank you for the response and the link, but I’m still unsure how to resolve this issue. I've thoroughly reviewed my account and folder settings, but I can’t find any restrictions or settings that would explain why this error is occurring.

What I find particularly confusing is that the API calls were working fine yesterday, and now, without any changes on my end (even for files in my personal account not in a shared folder), I’m seeing this not_allowed error.

Could you please clarify:

Where can I check or modify settings that might be restricting the ability to generate temporary links?
Why would this issue suddenly occur when no settings or permissions were changed on my side?
Any specific guidance on what settings or configurations I should adjust would be greatly appreciated.

I suggest contacting support to check on the state of your account, to see if/why your account's links are currently banned.

Funny you mention that—I tried upgrading my account today to resolve this issue, but now I can't access the plan/billing section of my settings, and I'm also told I can't contact support because of my plan status, even though I upgraded. I believe there was a glitch, as I was on a Standard trial and attempted to upgrade to a Professional account. Can you please help me with this?

If you're currently unable to use the standard support page, use this API support form and reference this forum thread; we'll redirect your ticket accordingly.