Bash Script - Curl (Filename Too Long Error)

Please read carefully, otherwise i dont answer auto bids.


I get error FILE NAME TOO LONG

#!/usr/bin/bash

BACKDIR=/home/ykose/yedekBOX
DATE=`date +'%m-%d-%Y'`
WPDOSYA=`for file in $BACKDIR/*$DATE.sql.gz; do echo "${file}"; done`
BASE64=$( base64 $WPDOSYA -w 0)

curl -X 'POST' \
'http://127.0.0.1:5555/api/whatsapp/send-file-base64' \
-H 'accept: /' \
-H 'Authorization: Bearer $2b$10$DQmaItvVtZUUpEDCwGLPCOazPAms02NytCa81uWTQgVqJcS4_5g4m' \
-H 'Content-Type: application/json' \
-d @< '{
"phone": "999999999",
"filename": 'test.pdf',
"base64": "data:file/pdf;base64", '$BASE64',
"isGroup": "false"
}'

How can i fix the FILE NAME TOO LONG error?

$20 for the correct answer.