What is the ruling of Islamic law on working in marketing to sell company shares and domains online for a percentage of the selling price, or buying and trading these shares?

The ruling on buying shares or working in their promotion is based on the nature of the companies: If they are permissible and do not deal with usury (riba) or prohibited matters, then it is permissible to buy and work with them. However, if they are usurious or deal with prohibited matters, then it is not permissible to buy or promote them, due to Allah Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." As for the margin system, if it deals with usurious banks, or violates the conditions of exchange, or involves ambiguity (gharar), ignorance (jahalah), or usury, then it is not permissible to deal with or promote it; otherwise, it is permissible.