The message is too large for the tag
Four ways out, and buying a bigger tag is the last of them. Trim the content, drop the parameters, move everything to a server behind a short address, and only then consider more memory. The first three cost nothing and usually work better.
Measure before deciding
Read a blank tag from the same batch and note the free space it reports. That is the number to work against, not the capacity on the packaging.
Then measure the content you are actually writing, including everything appended to it. Tracking parameters on a web address are regularly longer than the address itself.
The gap between the two is what you need to close, and knowing it turns a vague problem into an arithmetic one.
A write that exceeds the free space is rejected rather than truncated, so the tag keeps whatever it had and nothing is silently lost.
Trim what you are writing
Remove records you do not need. A tag carrying a web address and a text label is carrying two record headers as well as two payloads.
Shorten the path. It is written character by character, so a shorter path is directly fewer bytes.
Cut contact card fields to the ones that matter. Every field is bytes, a longer tap, and one more thing to become wrong.
Avoid accented and non Latin characters where an unaccented form is acceptable, since they cost more than one byte each.
Move it to a server
This is the answer that removes the problem rather than easing it.
Write a short address on a domain you control. Hold the content, the parameters and the logic on your server. The tag then carries a few dozen bytes and fits on the cheapest chip sold.
It also makes the content changeable after deployment, which no amount of tag memory offers.
The exception is a tap with no network, where the content genuinely has to be on the tag. That case is real and it is a minority, so establish whether you are in it before buying anything.
When to buy more memory
When the content must work offline and cannot be shortened further. That is the honest case and it is worth paying for.
When you need several records and each one is necessary.
Size against measured free space with margin for a later correction, since a tag written to its exact limit cannot absorb one added character.
And remember that more memory changes nothing else. It reads no further, no faster and no more reliably, so it is worth buying only for the room.
Frequently asked questions
Does the tag truncate my message?
No. A message larger than the free space is rejected and the previous content stays, so nothing is silently cut.
Why does the packaging say more than the tool?
The packaging states total memory, and the tool reports what is left after the fixed structure and the formatting. Work against the tool's figure.
Will a bigger tag read as far?
Range follows antenna size rather than memory, so a bigger capacity in the same size of tag reads the same.
How much margin should I leave?
Enough to absorb one realistic correction, such as a longer path or an extra field. A tag at its exact limit cannot be edited later.