Invalid parameter number in PHP 8 with whereIn

Hi everyone I hope that you are well. I am having a bit of an issue since upgrading to PHP 8. I am using a whereIn DB query - which was working fine in PHP 7.4. But is now giving errors:

Invalid parameter number (SQL: select * from `plat_touchpoints` where `touchpoint_id` in (3.1))

The call is as follows:

$touchpoints = \DB::connection('bf_remote_platform')->table('plat_touchpoints')->whereIn('touchpoint_id', $array)->get();

It works fine with pulling items upto 3, but anything more than that it throws an error as above and this is only in PHP 8 that I am experiencing this. Any help or guidance will be much appreciated.