Which of the following is not an essential condition for interference?

When two waves come together, they can interfere constructively or destructively. To set a stable and clear interference pattern, two conditions must be satisfied, they are, the sources from which waves are coming must be coherent. Coherent waves means they will have constant phase difference. Next condition is the source from which the wave is propagating must be monochromatic, all the waves will be having the same wavelength and frequency.
The amplitude must be the same for two waves is not a required condition for waves to interfere constructively or destructively.