Excel tells my formula in new name in name manager has a problem

So, I've been following a guide on how to create an invoice with excel on youtube (can't show you the exact video cause my account is fairly new, but it's the most famous one by the youtube channel: excel for freelancers)

At around the 14 minute mark he says to put a formula in the'refers to' bar, namely the following formula: =OFFSET([tabname]!$A$2,1,,COUNTA([tabname]!$A$2:$A$999)-1,1
If I type the EXACT same thing in my formula bar it says that there is something wrong with my formula. I've noticed that I'm using a different excel than in the video, but the video is not THAT old

Feeling I'm missing something... But not sure what
Anyone know what to do? Thanks in advance

When you have an exclamation mark ( ! ) in a range, that means that whatever is in front is a sheet ( or tab ) name. So, maybe, something like Sheet1. If the sheet name has any spaces in it, you have to put single quotes ( ' ) round it. Something like 'Test Sheet 1'.

It als looks as though you are missing a closing bracket.

Which probably means your formula should be, for example,

Formula:

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Could you attach a screenshot?

Try:
=OFFSET(Sheet1!$A$2,1,,COUNTA(Sheet1!$A$2:$A$999)-1,1)

But I prefer:
=Sheet1!$A$3:INDEX(Sheet1!$A:$A,COUNTA(Sheet1!$A:$A))

Administrative Note:

Members will tailor the solutions they offer to the version of Office (Excel) that you have. Please check that your forum profile is up-to-date in this respect - 2111 is a release number, not the version per se. If you aren't sure, in Excel go to File | Account and report what it says below the MS logo at the top of that page. If your version is for Mac, please also state this. Thanks.

Given that you are in the Netherlands, I'd bet you need semicolons, not commas, in that formula.

Please update your profile with the correct version of Office, as requested above. Thanks.