When you have finished to serve a plane you will earn “wollars” everytime. The value you can see, if you choose an airplane at the left top edge in the green field (2504 Wollars).
The status of the contract cann you see in the field below of the airplane picture, at the “Vertragsatministrator” (contract administrator). In my example i have done 2 landings from 5 required.
When you have fullfilled the contract this lokes like the next picture for example:
Now you can see 2 green little planes from 2 required, so the contract ist finished and you can collect the rewards. In this case you get XP and Silverplanes (SP), like the next picture shows:
When you have collected you can improve/extend (Verbessere den Vertrag) or cancel (Abbrechen) the contract. When cancel, you can choose a new contract at airports the plane can reach from the map. But consider, the new contract beginn with one required landing an less XP and SP as reward!
When you improve the contract, the required landings will be increased by one, so after that, there will be 3 grey little planes at the contract admin. Improvement is allways possible after each finished contract. The required amount for landings increase each time by one, but only up to maximum 10 required landings.
Now you can also see the amount of wollars you will earn when you have done the service:
When you have finished a contract in the highest contract level (10 landings) you can improve the contract again, so the contract starts with 10 required Landings immediately. So it´s possible to earn the maximum amount of XP and SP, but its a lot work up to this point.
You can earn faster XP and SP, when you select the player contracts, because the contracts beginns with 10 required landings immediately. So you are able to earn the maximum value of XP and SP very soon!
The last info i will post here is, how you can find all the rewards for a contract. Look at the forum at FAQ, like here:
How to find all the rewards for a contract - FAQ’s & How to play / How to… - World of Airports forum
I hope i could help you!
have fun, have a nice day and see you in the skys