Did you changed anything (and I even mean a PHP re-installation or server configuration) that could interfere with the the application or it's code itself?
Can you post your code? (The request part is necessary only)
Error 403 - when accessed from php
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Nov 19, 2020
0
#3
We all had. Two weeks ago there was a note posted by Ben explaining that somebody was flooding the system with calls and not responding to requests. Therefore we were all being throttled.
Nov 19, 2020
0
#5
By the person who is deliberately causing the problem, stopping overloading the system, and responding to communication from staff.
I agree. I think the issue is related with too many requests from your client (check: https://en.wikipedia.org/wiki/HTTP_403 ). Despite there is a special code for this situation (429 if I remember it right), I guess that reduction of your request rate shall solve the issue ( https://www.w3schools.com/Php/func_misc_sleep.asp ). Don't be greedy. 
Second possible interpretation: I experience some small problems with the web-site now, so maybe it is also reflected in API accessibility.
About a week ago I started to receive 403 error for all calls to player resources.
Other resources like club matches, club members etc. works without issue.
API accessed directly from browser (ie. https://api.chess.com/pub/player/0nvm) works fine, but if accessed from the applications it fails with 403. Last attempt was right now at 5:52pm UTC.
Does anybody have the same problem?
@erik, @bcurtis: is it possible to check the issue?
Thanks in advance.