PHP message: WordPress database error You have an error in your SQL syntax

Καλησπέρα και ευχαριστούμε για το θαυμάσιο plugin.

Έχω εγκαταστήσει το plugin σε κάποιο e-shop, και βρίσκομαι στο στάδιο των δοκιμαστικών συναλλαγών.

Πιο συγκεκριμένα, κατά τη διάρκεια δοκιμής επιτυχούς συναλλαγής, διαπιστώνω οτι, ενώ η συναλλαγή γίνεται με επιτυχία στην Πειραιώς, δεν γίνεται redirect στο δηλωμένο page, ούτε αλλάζει το status της παραγγελίας. Τα logs δείχνουν:

Date	Type	IP	Code	Message	Ref	Size	Source
2/7/2020 14:45	Access	93.113.216.129	200	GET /checkout/ HTTP/1.1	https://lappelduvide.gr/product-category/dresses/	40.4 K	Apache SSL/TLS access
2/7/2020 14:45	Access	83.169.34.200	200	POST /wp-cron.php?doing_wp_cron=1593693937.0152690410614013671875 HTTP/1.1	https://lappelduvide.gr/wp-cron.php?doing_wp_cron=1593693937.0152690410614013671875	5.80 K	Apache SSL/TLS access
2/7/2020 14:45	Access	93.113.216.129	200	POST /?wc-ajax=update_order_review HTTP/1.1	https://lappelduvide.gr/checkout/	15.8 K	Apache SSL/TLS access
2/7/2020 14:45	Access	93.113.216.129	200	POST /?wc-ajax=checkout HTTP/1.1	https://lappelduvide.gr/checkout/	875	Apache SSL/TLS access
2/7/2020 14:45	Access	93.113.216.129	200	GET /checkout/?key=wc_order_ShKPZY3ccMyEh&order-pay=8243 HTTP/1.1	https://lappelduvide.gr/checkout/	32.8 K	Apache SSL/TLS access
2/7/2020 14:46	Access	93.113.216.129	200	POST /wp-admin/admin-ajax.php HTTP/1.1	https://lappelduvide.gr/wp-admin/admin.php?page=wc-settings&tab=checkout&section=piraeusbank_gateway	888	Apache SSL/TLS access
2/7/2020 14:46	Access	83.169.34.200	200	POST /wp-cron.php?doing_wp_cron=1593693998.1581048965454101562500 HTTP/1.1	https://lappelduvide.gr/wp-cron.php?doing_wp_cron=1593693998.1581048965454101562500	5.80 K	Apache SSL/TLS access
2/7/2020 14:46	Access	83.169.34.200	200	POST /wp-admin/admin-ajax.php?action=as_async_request_queue_runner&nonce=12396f0033 HTTP/1.1	https://lappelduvide.gr/wp-admin/admin-ajax.php?action=as_async_request_queue_runner&nonce=12396f0033	5.96 K	Apache SSL/TLS access
2/7/2020 14:46	Access	93.113.216.129	301	POST /wc-api/WC_Piraeusbank_Gateway?peiraeus=success HTTP/1.1	https://paycenter.piraeusbank.gr/Redirection/(S(5iroak3goxxfy3k3t4tkmsvx))/ResultPages/Results.aspx?Success	6.23 K	Apache SSL/TLS access
2/7/2020 14:46	Access	93.113.216.129	302	GET /wc-api/WC_Piraeusbank_Gateway?peiraeus=success HTTP/1.1	https://paycenter.piraeusbank.gr/Redirection/(S(5iroak3goxxfy3k3t4tkmsvx))/ResultPages/Results.aspx?Success	419	Apache SSL/TLS access
2/7/2020 14:46	Access	93.113.216.129	200	GET /checkout/ HTTP/1.1	https://paycenter.piraeusbank.gr/Redirection/(S(5iroak3goxxfy3k3t4tkmsvx))/ResultPages/Results.aspx?Success	40.4 K	Apache SSL/TLS access
2/7/2020 14:46	Error	93.113.216.129		AH01071: Got error 'PHP message: WordPress database error You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 3 for query SELECT trans_ticket\n\t\t\tFROM <code>gx5eTTCc_piraeusbank_transactions</code>\n\t\t\tWHERE <code>merch_ref</code> = \t; made by require('wp-blog-header.php'), wp, WP->main, WP->parse_request, do_action_ref_array('parse_request'), WP_Hook->do_action, WP_Hook->apply_filters, WC_API->handle_api_requests, do_action('woocommerce_api_wc_piraeusbank_gateway'), WP_Hook->do_action, WP_Hook->apply_filters, WC_Piraeusbank_Gateway->check_piraeusbank_response\n', referer: https://paycenter.piraeusbank.gr/Redirection/(S(5iroak3goxxfy3k3t4tkmsvx))/ResultPages/Results.aspx?Success			Apache error
2/7/2020 14:46	Access	93.113.216.129	200	POST /?wc-ajax=update_order_review HTTP/1.1	https://lappelduvide.gr/checkout/	15.8 K	Apache SSL/TLS access

Το WordPress Status δεν δείχνει κάποιο πρόβλημα.

Θα εκτιμούσα οποιαδήποτε βοήθεια. Ευχαριστώ.