Please Help Needed - provision custom server with laravel forge

Hi,

Having a headache with provisioning with forge then installing git repo.

This is what I do.

1. Spin up my own EC2 server.
2. Use Forge API to create a custom server in Forge and obtain a provisioning script.
3. SSH to the server (via code) and run the provisioning script.
4. 10 Minutes later the server is provisioned
5. Then I try to install git repo either via api or forge UI and it just wont work. It says

Cloning into 'default'... Host key verification failed. fatal: Could not read from remote repository.

Please make sure you have the correct access rights and the repository exists.

The main problem I think.. is step 3. If I manually SSH into the server myself and then run the script, after provisioning is complete I can install the git repo via the forge UI or via API. Only when I use code to SSH and run the script it wont install the repo.

I think its really weird that it wont install, because the provisioning completes. It sends me an email as normal and in Github the deploy key is set up.

I am using phpseclib to SSH into my server code below:

        // SSH to server
        $key = new RSA();
        $key->loadKey($myKeyFile);
        $ssh = new SSH2($serverIp);
            
        if(! $ssh->login('ubuntu', $key)) {
            throw new Exception('SSH exception - unable to gain access to server via SSH');
        }

        // Execute provisioning script
        $ssh->exec('the-script-obtained-from-forge-here');

This all executes and the server provisions. So what Am I doing wrong? I contacted Forge support and have been told to check my code, but i'm stuck. I cant understand why it will work when manully SSH but via phpseclib is doesn't.

If any anyone can help I will be really grateful.

Thanks.