IMAP multiple searches - array_intersect and PHP 7.4 Problem

I need to do a multiple search on an email box. I am using PHP 7.4.
I know imap has  a problem with multiple search criteria from everything I have read.
So I thought I would issue a search for each criteria and then use array_intersect  with the results of each  search giving me exactly what I want.
I want to select only emails that match a 'from' email address and the subject line is 'INVOICE'
The 'from' address will vary - it's read from a table.
But I can not seem to get the syntax correct.  I keep receiving: Notice: Undefined variable: emails.
And it should contain two valid email that match the search criteria of the 'from' address and the subject line  'INVOICE'. But it does not work.
Any help appreciated. And thank you in advance.

 $strFromEmail  = 'testir@gmail.com';

 $arrayFrom = imap_search($inbox, 'FROM "' .  $strFromEmail . '"'', SE_UID);
 
 $arrayInvoice = imap_search($inbox, 'SUBJECT "INVOICE"', SE_UID);
 
 if((!empty($arrayFrom)) && (!empty($arrayInvoice)))
 {
   $emails = array_intersect($arrayFrom, $arrayInvoice);
 }

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