Adding refridgerant 134a to 2001 xj8 with A/C PRO

Same thing on my 04 x-type, as i found yesterday on my 01 xj8, and that is the low port side will not accommodate the nozzle from the a/c pro can. On my x type i have to hold it down to get a couple squirts
in which was enough, but i guess i assumed these cans are supposed to latch on correctly???