I cant install recovery and ROMs

I have a galaxy s5 G900F and i tried to install a ROM. I rooted the phone ( i think I have Rootchecker says its rooted). I tried every recovery i found to install but none worked. When i try to enter recovery the screen just goes black. I managed to install 1 recovery and enter it i think its TWRP 3.0.2 but when i tried instaling a ROM there was an error 7. Can someone pls tell me what I need to do. My android is 6.0

And I've had a Htc One X and S3 and I had noo problems instaling ROMs there.

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