Okay so your url is definetly malformed, if you have verified the ids against shopify and you know them to be correct then either your store name-myshopify.com, APIkey or password are incorrect / transposed. The url should be buit in this order
protocol (example) "https://"
apiKey (example) "3048432098244820598250"
":"
password (example) "290839820984049820598524098/"
shopname (example) "storename.myshopify.com/"
'admin/orders/'
orderid (example) "450789469/"
'fulfillments/'
'fullfillment_id.json' (example) "255858046.json"
when I look at your url string it looks sound but then perhaps you have the password and APIkey switched around, APIkey first. Also make sure you are using your private app password not a shared secret. Also double check your shop name. I can 't check this for you because of security reasons but just double check that those values are correct and that if you say
echo $complete_connection_url_string_name;
exit;
that what is printed is as it should be. you should be able to copy it and paste it into your address bar and get a result that isn't an error.