Substitute function not working with commas

I have the following which i saved as a process variable of type text

{ "userId": "abc123", "submissionId": "111222333", "createdDt": "2022-06-17T04:07:19.611Z"}

I want to remove spacing between the commas and colons, trying to do so with substitute(pv!text, ": ", ":") and substitute(pv!text, ", ", ","). It works for the colon, but not for the comma, so the result is the following

{ "userId":"abc123", "submissionId":"111222333", "createdDt":"2022-06-17T04:07:19.611Z"}

Also, when i use stripwith(pv!text,","), the comma can be affected and removed. Wondering why substitute cant do the same.

Any ideas as to why this is happening or how else I can remove the space between the comma?