Thank you for your post, and I apologize for the late reply.
We are aware of the ~ and $ issue in URLs, as this also occurred in FileMaker Go 13. One of the developers mentioned that this is case sensitive, so if the file is all lowercase letters, and you specify one uppercase character, this will fail. The workaround to use encoded characters for $ (%24) and ~ (%7e) is acceptable.
I have attached your post to the original report. When more information becomes available, I will post again.
When I searched the Known Bugs List, I found a number of entries dealing with FMP URL's but none seemed to exactly match this issue.
An entry in the Known Bugs List has been linked to this Issue Report. Any Comments/Questions/Suggested Corrections should be posted here or in a new thread. Please do not post such comments to the Known Bugs List thread.