If you mean you need a dedicated IP address, then you can’t have a dedicated IP address on free hosting. Infinityfree is a free shared hosting.
For a dedicated IP Address, you need premium hosting with a dedicated IP Address purchased separately or a VPS or Dedicated Server to have a dedicated IP Address.
However, regarding this issue, I don’t think a shared IP Address is the issue.
As mentioned by @Greenreader9 you must contact their support team regarding this issue.