The code example in the documentation, that you are referring to, is bad PHP. You need to actually make the tags element an array and pass in each tag you want to use.
Pass a string (for one tag) or an array (for multiple tags).
I managed to figure this out based on the way list work.
You need to number your tags and not use empty brackets. Not Like This
$post = array(
‘email’ => $contactData[5],
‘tags[]’ => $contactData[7],
‘tags[]’ => $contactData[8],
);
Biannca here from our CX team. I just wanted to update this thread for anyone that comes across this - we’ve updated our API to v3 and if you want to add multiple tags via API through PHP, you should be inserting something along the lines of: