UndefinedMagicMethod

Emitted when calling a magic method that does not exist

<?php

/**
 * @method bar():string
 */
class A {
    public function __call(string $name, array $args) {
        return "cool";
    }
}
(new A)->foo();

To fix, add all used magic methods as @method annotations:

<?php

/**
 * @method bar():string
 * @method foo():string
 */
class A {
    public function __call(string $name, array $args) {
        return "cool";
    }
}
(new A)->foo();

Or, only if dealing with generic wrapper objects (like FFI classes), use @psalm-no-seal-methods.
Try to avoid using @psalm-no-seal-methods, as it worsens type coverage, and is not needed in the vast majority of cases.