As being mentioned in the checklist for a Schengen visa, if purpose of the travel is to visit someone, an invitation letter from the inviting person is required. There are many samples of invitation letters on the Internet that you can download, but I preferred to write my own one to make sure that it must be a perfect formal letter with a right format.
In the invitation letter, the inviting person must mention clearly the relationship between the two, purpose of visiting, length of stay, where you are going to stay, and who is gonna pay for the travel.
We wrote one letter in English and another in German, and we’d love to share one with you for future reference. However, it was our personal situation,please do not copy exactly the same . You need to write your own situation and change the details. Then, put in faith and love 😛