Esp8266 d1 mini: espcomm_upload_mem failed

Hello everyone,
I don't know if that topic already exists or if I'm doing this right but if it does exist or if I do use the forum wrong then I'm extremly sorry!
To my Problem: I tried programming the Esp8266 d1 mini that I bought on AZ_Delivery and even though at first I had problems writing a working program I made it in the end!
The pride over finishing the program didn't last long.. When I wanted to upload the project to my esp i got following error:

error: failed reading byte

warning: espcomm_send_command: can't receive slip payload data

error: failed reading byte

warning: espcomm_send_command: can't receive slip payload data

error: failed reading byte

warning: espcomm_send_command: can't receive slip payload data

error: failed reading byte

warning: espcomm_send_command: can't receive slip payload data

error: failed reading byte

warning: espcomm_send_command: can't receive slip payload data

error: failed reading byte

warning: espcomm_send_command: can't receive slip payload data

error: failed reading byte

I then searched the whole Internet trying to find a solution but nothing worked! I have the driver installed, a flash button isn't installed on the esp, all wires are okay and I don't use any extra boards! The only thing i noticed is that the blue LED is only flashing up when I connect the esp to my laptop and when I pressed the reset button! I connected a Display (Oled 128x32) o to the esp because it should be a clock. (Just incase that this helpes)
I really have no clue of what I'm doing wrong. If anyone knows something then I will highly appreciate it if you would share your knownledge with me!

Thank you in advance, Ellie