does PPTP Server requires GRE srcnat masquerading ?

Hi
I have setup pptp server with ip pool, ppp profile, secret and pptp server and firewall filter rules for tcp port 1732 and protocol GRE
No client can connect to mikrotik pptp server, no problem woth other pptp servers on RP3B for example
TCP connection established from XX.XX.XX.XX

pptp logging show 7 times
<192>: sent LCP ConfReq id=0x7

and ends with
<192>: LCP lowerdown
<192>: LCP lowerdown
<192>: LCP down event in starting state

it looks like GRE rotocol cannot be setup
It is not due to my ISP provider, tried other RP3B pptp server behind it and it worked fine, so my ISP is not blocking anything

but the question is do i need to srcnat masquerade GRE protocol to outside in firewal nat rules and if so how do i do this ?
do i need to specify source address ranges ? connection type pptp for this masquerading ?

how does the GRE protocol goes back to the internet ?

i am not using a bridge as i cannot do so because of routing requirements

thx
chris

PPTP port is 1723. I have only this port open and no rules for GRE.

No special src-nat rules for PPTP. There is a helper for PPTP server behind NAT, ir takes te job: /ip firewall service-port