Double-check the file actually matches the source format for that tool, and try a recent version of Chrome or Firefox \u2014 a few formats (like AVIF export) depend on what your specific browser supports.
Everything runs on your device rather than a server, so very large batches on an older phone or laptop will take longer. Converting fewer files at once usually helps.
Correct \u2014 no account, no credits, no daily cap. Since conversion happens on your device, not ours, there\u2019s no server cost tied to how much you use it.