Introduce yourself and describe the project
Say what you play, where you would like to rehearse and what kind of project you have in mind. If you are still exploring ideas, say so. You do not need to look like a complete band to start meeting musicians.
Mention a real shared interest
Read the profile and listen to a video if one is available. Mention something specific that caught your attention: a shared style, an approach to playing or a similar goal. Avoid generic praise sent to dozens of people.
A template to make your own
Replace the bracketed fields with your own details and use only genuine references. You can propose an initial conversation; you do not need to ask for a commitment to the band immediately.
Leave room for a reply
Someone may be unavailable, prefer another style or simply not be interested. Respect that decision. If the reply is positive, agree on the purpose of the meeting, the rehearsal venue and what each person will prepare.
On PinMusic, you need a photo to send or reply to invitations. Keep your profile updated so the other person can get to know your sound too. Invitations have an initial message and a reply; they do not work as continuous chat.