A URL writes fine but Wi-Fi or a contact fails
Two causes, and size is the likelier one. Wi-Fi credentials and contact cards are far larger than a web address, so a tag with plenty of room for a link can have none for a contact. The other cause is a tool that writes only some types.
Size is the usual cause
A short web address is tens of bytes. Wi-Fi credentials and a contact card are hundreds.
So the same tag can accept one and reject the other, and the refusal looks like a type restriction when it is arithmetic.
Read the tag for its free space and compare it against the record you are trying to write. If the record is larger, that is the answer and no tool will change it.
A contact card with many fields, or with an embedded image, is far larger again and fits on no tag at all.
The tool may not offer it
Writing applications differ in which record types they support. A tool that writes addresses and text may have nothing for Wi-Fi or contacts.
The refusal then comes from the application rather than the tag, and it is easy to mistake for a tag limitation.
Check whether the type is offered at all before concluding anything about the tag. If it is not in the list, the tag was never asked.
Platform differences
Writing a record and having a phone act on it are different questions, and the second differs between platforms.
Wi-Fi credentials are the clearest example: written to a tag they configure a network on Android and are not acted on the same way by an iPhone. The record can be written successfully and still do nothing on half your audience.
So a successful write is not the end of the test. Tap the tag on both platforms and watch what actually happens.
For anything aimed at the public, this is a strong argument for a web address, which is the type handled most consistently everywhere.
What to do instead
If the record does not fit, write a short address and put the content on a page. Wi-Fi details and contact details both work perfectly well delivered that way, and they stay correctable.
If the tool does not support the type, use one that does, and verify the result rather than trusting that it wrote what it claimed.
If the platform will not act on it, decide whether half your audience is acceptable. Usually it is not, and the address is the answer again.
Keep the offline case in mind. Where there is no network at the point of tap, the record has to be on the tag, and then the size question becomes a purchase decision.
Frequently asked questions
Why does a URL write and Wi-Fi does not?
Usually size, since Wi-Fi credentials are several times larger than a short address. Read the tag's free space and compare.
Can any tag hold a contact card?
Not the smallest ones. A useful contact card is several hundred bytes, which needs a mid range chip at least.
Will a Wi-Fi tag work on iPhone?
It can be written and iOS does not act on it the same way Android does. Test on both before deploying to the public.
Is a link as good as an embedded contact?
Better in most cases, since it fits anywhere, taps faster and stays correctable. The exception is a handover with no network.