bash script can't find source file in script running in systemd

I have set up a systemd.service that starts a bash script when the system boots. The script starts, but it seems that it cannot find the referenced source files but when i start the same script from the terminal i works fine. Al scripts are in one and the same directory.

Anyone have any suggestions to fix this?

systemd.service file:

[Unit]
Description=RIB
After=network-online.target

[Service]
Type=simple
ExecStart=/home/user/release/.scripts/start-script.sh start
Restart=on-failure

[Install]
WantedBy=multi-user.target

part of the start-script.sh

#!/bin/bash

source config.sh
source function.sh


check_connection #function

# GET LOCATION IN .JSON FILE
get_location #function
if [[ $? -ne 0 ]]
then
    printf "%s\n""Can't get location\n\n"
else
    printf "%s\n""Location successfully retrieved\n\n"
fi

source config.sh:

version="2021.01.25"
date=`date '+%Y-%m-%d %H:%M:%S'`
time=`date '+%H:%M:%S'`
temp_path="/home/$USER/temp"
release_path="/home/$USER/release"
info_path="$release_path/to/info"
content_path="$release_path/to/content"
ftp_url="ftp.test.com"

source function.sh:

function check_connection ()
{
    printf "%s\n""${Green}Check connection with $ftp_url.${Color_Off}\n\n"
    while ! timeout 0.2 ping -c 1 -n $ftp_url &> /dev/null
    do
    printf "%s\n""${Green}RIB cannot reach $ftp_url, check WIFI connection.${Color_Off}\n\n"
    sleep 5
    done
    printf "%s\n""${Green}RIB can reach $ftp_url.${Color_Off}\n\n"
}