transactions.html can edit though needs some kinda user feedback of the changed row or something...

cmd/http/router.go

@@ -4,6 +4,7 @@ import (
 	"embed"
 	"encoding/json"
 	"fmt"
+	"io"
 	"io/fs"
 	"net/http"
 	"os"
@@ -110,7 +111,21 @@ func (router Router) APITransactions(w http.ResponseWriter, r *http.Request) {
 }
 
 func (router Router) APIAmend(w http.ResponseWriter, r *http.Request) {
-	http.Error(w, http.StatusText(http.StatusNotImplemented), http.StatusNotImplemented)
+	b, _ := io.ReadAll(r.Body)
+
+	var req struct {
+		Old ledger.Delta
+		Now ledger.Delta
+	}
+	if err := json.Unmarshal(b, &req); err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+
+	if err := router.files.Amend(req.Old, req.Now); err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
 }
 
 func (router Router) APIReg(w http.ResponseWriter, r *http.Request) {