Please where are our knowledgeable German based guys. What do i need to send invitation letter for a visiting visa. I heard of three months payslip, house contract. My question is if the house contract has to be recognized by the size of the apartment or just any house contract. Secondly, must i have permanent residence permit or just residence permit?
. Thanks in advance.

I am still waiting for this information?

Still on it.

Basically what you need are the following:
1.The three months payslip true but it has to be able to reach the from the foreign office requested height i.e you have to earn enough for you to be allowed to invite somebody. and the money is pegged at a certain amount, it depends on which bundestadt that you live in so it is always different . you can get this from your sadt foreign office.
2.Vepflichtungeklarüng i.e declariotion of obligation to your guest which means you are commiting yourself to carry any financial obligation your guest my incur.
3 Krankenversicherung you kann get this from ADAC or other insurance companies this is needed in lieu that maybe you guest can while he or she is visiting could get sick and it will be covered by the insurance so that you will not have course to recourse to stadt money
4. To 1 above you also have to have enough wohnraum (Living space) for your guest to stay or you get an hotel booking prepaid with the hotel receipt attached.
5. you don't need to have a permanent residence permit your Befristete Residence Permit is enough as long as you fulfil the other required criterias

Thanks alot for ur input, but please while i was going through their website i saw where it was written that i dont need hotel reservation for a family member who is visiting me. That it must be a wohnung or something like that. I have a wohnung but the qm is even small for my family living here already. So what is the way out.

On krakenversisherung, the part i am living, we are all using Aok and i heard they are the best but another question is what if the visitor is already sick, will he be able to receive treatment with his krakenversicherung? If not what is the way out again?

You have already answered your own question if the Appartment is too small you have no other way than to invest in an hotel because for every individual it is assumed that a 12qm space is needed.
The Krankenversicherung i.e Health insurance is not for you but your guest and the price also depends on the age of the invitee (when older a little bit more expensive the reason ADAC) your AOK will not cover your guest.
To your guest being sick it is a tough one because no insurance wants to pay. You will be made to pay cash when you go with your guest to a doctor and claim it later from the insurance and i have not seen anybody up to date that was succesful why, because they will claim the sickness did not happen in Deutschland but she had it already so they are not liable. unless you are bingeng your guest as per Medicine check which is going to cost you heavy

Thanks alot