I've uploaded my resource pack into Dropbox and changed it so it's a direct download link. Then I entered the same website address into "resource_pack=" in the server.properties file. Whenever any body joins, it requests them to download the resource pack and install it. Even if they accept, the resource pack doesn't appear to be downloaded.

This was also further tested in 1.12 with a 1.12 - Compatible Resource Pack, this was not the case. I tested a 1.13 Server with a 1.12 Resource Pack, even though it was incompatible, the resource pack still downloaded.

I tried the opposite, A 1.12 Server with a 1.13 Resource Pack, it didn't download. I checked the link and re-uploaded the file multiple times, but no solution,

Keep In Mind That This Bug is From 1.13 - 1.14.4

For Further Investigations, I have provided the direct download links to both my 1.12 and 1.14 resource pack:

1.12: https://www.dropbox.com/s/59o4m4e0u6pycrn/AlSh_7i%20Faithful%20U0%20-%201.12.zip?dl=1

1.14: https://www.dropbox.com/s/c61uir9rzjno31u/AlSh_7i%20Faithful%20%26%20Sounds%20Mix%20U2%20-%201.14.zip?dl=1